FIG. 1 shows an example of a conventional bearing structure used for axles of a truck. An axle 1 has ends each of which rotatably supports, via a unit bearing 3, a hub 2 for mounting of wheels (not shown). The unit bearing 3 is a preliminarily unitized assembly comprising an inner race 5 fitted over a rod 4 which in turn is protruded from the end of the axle 1 outward in a vehicle-width direction (right in FIG. 1), rollers or other rolling bodies 6 rotatably on an outer periphery of the inner race 5, an outer race 7 encircling the outer periphery of the inner race 5 to rotatably carry the rolling bodies 6 and oil and dust seals 8 and 9 as seal members for closing a gap between the outer and inner races 7 and 5 oppositely in the vehicle-width direction to enclose grease (not shown) in the gap.
The unit bearing 3 is press-fitted to an inner periphery of the hub 2 such that the outer race 7 is tightly fitted with the inner periphery of the hub 2; and a portion of the hub 2 inward in the vehicle-width direction (left in FIG. 1) is formed with an abutment 10 on which the outer race 7 of the unit bearing 3 abuts for positioning.
The inner race 5 is clearance-fitted (loose-fitted) over the rod 4 of the axle 1 in consideration of workability, the inner race 5 abutting at one end thereof on a step 11 of the rod 4 and being clamped and fixed at the other end thereof by a spindle nut 12 through a washer 12a. The washer 12a has an inner periphery from which a number of stops (not shown) are projected at required peripheral positions and are fitted into corresponding grooves (not shown) on an outer periphery of the rod 4, so that even in case the inner race 5 is rotated relative to the rod 4 and its rotational force is transmitted to the spindle nut 12, the spindle nut 12 is prevented from being loosened.
Inserted into the axle 1 from the rod 4 side is a drive shaft 13 for rotation of the wheels (not shown) together with the hub 2. The drive shaft 13 has an end away from an inserted end thereof and formed with a flange 13a which in turn is fixed on an outer side surface of the hub 2 by an bolt or other fastening member or members (not shown).
The dust seal 9 in the unit bearing 3 inward in the vehicle-width direction serves not only for enclosing the grease inside but also for preventing outside water and foreign matters from invading. The oil seal 8 outward in the vehicle-width direction serves also for preventing differential oil 14 as lubrication oil, which leaks from a gap between the rod 4 of the axle 1 and a shaft portion 13b of the drive shaft 13, from invading into the unit bearing 3.
Further, mounted on the flange 2a of the hub 2 at surfaces thereof outward and inward in the vehicle-width direction are tire wheels 15 and a brake drum 16, respectively, by bolt and nut or other fastening members 17. Incidentally, illustrated in FIG. 1 is a dual-tire mode in which two tires (not shown) are mounted on the hub 2 on each side thereof in the vehicle-width direction through the tire wheels 15. The surface of the hub 2 inward in the vehicle-width direction is formed, at peripheral positions, with lightening depressions 18.
General state of the art pertinent to the bearing structure as mentioned in the above is shown, for example, in Patent Literature 1.
FIG. 2 shows an example of an independent suspension structure on a front side (steering wheel side) in a truck or the like. In FIG. 2, reference numeral 101 denotes a knuckle connected with a tie rod (not shown) for an steering operation. The knuckle 101 has a spindle 102 which is encircled by and rotatably supports, via a unit bearing 104, a hub 103 for mounting of a wheel (not shown).
The unit bearing 104 is a preliminarily unitized assembly comprising an inner race 105 fitted over the spindle 102 of the knuckle 101, rolling bodies (rollers) 106 rotatably on an outer periphery of the inner race 105, an outer race 107 encircling an outer periphery of the inner race 105 to rotatably carry the rolling bodies 106 and oil and dust seals 108 and 109 as seal members for closing a gap between the outer and inner races 107 and 105 oppositely in the vehicle-width direction to enclose grease (especially not shown) in the gap.
The unit bearing 104 is press-fitted to an inner periphery of the hub 103 such that the outer race 107 is tightly fitted with the inner periphery of the hub 103; and an outward portion of the outer race 107 in the vehicle-width direction (right in FIG. 2) is formed with a locking part 110 which engages with a step 102a on an inner periphery of the hub 103 for positioning.
The inner race 105 is clearance-fitted (loose-fitted) over the spindle 102 of the knuckle 101 in consideration of workability, the inner race 105 abutting at one end thereof on an abutment 111 of the knuckle 101 and being clamped and fixed at the other end thereof by a spindle nut 112.
Fixed in a press-fit manner on an outer periphery of an inward end of the hub 103 in the vehicle-width direction (left in FIG. 2) is a pulsar ring 113 formed with a number of teeth 113a on a side surface thereof toward inward in the vehicle-width direction. Passing of the teeth 113a of the pulsar ring 113 is detected and counted by a non-contact sensor (not shown; arranged in a phase different from the section shown) which grasps the passing as, for example, change in magnetic field, whereby number of revolutions of the wheel may be monitored.
Specifically, vehicles nowadays are provided with an antilock brake system (hereinafter referred to as ABS) for prevention of wheels from being locked in a braking operation. This kind of ABS requires to monitor any change in number of revolutions of a wheel upon braking operation to control the braking force, so that the hub 103 rotating in unison with the wheel is provided with the pulsar ring 113.
Further, the knuckle 101 facing the pulsar ring 113 in the vehicle-width direction is provided with a spider 115 for support of a brake shoe 114. Mounted on the hub 103 outward in the vehicle-width direction is a brake drum 116 to which the brake shoe 114 is pushed to produce the braking force.
In the example illustrated, the spider 115 has an inner periphery formed with a step 115a which has a required clearance to and assuredly prevents interference with the pulsar ring 113.
As a prior art literature pertinent to this kind of bearing structure, there already exists, for example, the following Patent Literature 2.